There is currently known in the prior art a wide variety of bicycles which include shock absorbing rear assemblies. Such bicycles typically include a main frame which comprises an elongate top tube rigidly secured to and extending between a head tube and an elongate seat tube. The head tube provides a structural base for the stem of the bicycle which has the handle bars attached thereto. The seat tube itself provides a base for a seat post which is generally telescopically received thereinto and to which is secured the saddle or seat of the bicycle. In the main frame, the seat tube includes a generally cylindrical bottom bracket shell attached to the bottom end thereof. The bottom bracket shell accommodates the crank assembly of the bicycle. The crank assembly itself comprises a bottom bracket spindle which includes a pair of cranks and a chain wheel attached thereto. Rigidly secured to and extending between the head tube and the bottom bracket shell is an elongate down tube of the main frame.
The shock absorbing rear assemblies of the prior art bicycles take on a wide variety of different configurations. In one commonly used configuration, the rear assembly comprises a pair of chain stays, the front ends of which are pivotally connected to the main frame. The back ends of the chain stays are attached to respective ones of a pair of drop-outs which accommodate the axle of the rear wheel. Also attached to respective ones of the drop-outs are the bottom ends of a pair of seat stays or swingarms, the top ends of which are attached to one end of a shock absorber. The end of the shock absorber opposite that attached to the swingarms is itself attached to a portion of the main frame. The shock absorber is actuated by and effectively dampens the upward travel of the rear wheel axle as occurs when the rear wheel encounters a bump or other obstruction.
As previously indicated, the above-described rear assembly is exemplary only, in that many variations of shock absorbing rear assemblies exist in the prior art. In this respect, certain rear assemblies include an additional link which extends between the swingarms and the main frame, with the shock absorber itself extending between such additional link and the main frame. The common characteristics of all shock absorbing rear assemblies is that they include the rear wheel rotatably connected thereto and are movable independently of the main frame for purposes of facilitating the actuation of the shock absorber and the dampening of the upward movement of the rear wheel.
Those prior art bicycles including shock absorbing rear assemblies possess certain deficiencies which detract from their overall utility. One such deficiency is attributable to the lack of efficiency in the transmission of energy from the rider to the rear wheel of the bicycle. This lack of efficiency occurs as a result of the crank assembly not being independently suspended relative to the main frame and rear assembly. Due to this lack of independent suspension, when the rider mounts the bicycle and begins pedalling, the pedalling force exerted by the rider is initially absorbed by the shock absorbing rear assembly to facilitate its actuation to an equilibrium position. It is only after the rear assembly is actuated to its equilibrium position that the pedalling force is translated into the forward acceleration of the bicycle.
A further deficiency with prior art bicycles including shock absorbing rear assemblies which is attributable to the lack of an independently suspended crank assembly is the tendency for pedal "kick-back" to occur when the rear assembly, and in particular the rear wheel thereof, encounters a significant bump or other obstruction. In the prior art shock absorbing rear assemblies, the chain extending between the crank assembly and the rear wheel is used to over constrain the suspension system when the rear wheel undergoes a moderate to significant amount of upward travel. Since the suspension system is over constrained by the chain, further upward movement of the rear wheel beyond a certain threshold necessitates that the chain rotate the chain wheel of the crank assembly backward. Since the chain wheel is attached to the pedals via the bottom bracket spindle and cranks, the backward rotation of the chain wheel results in the application of a kick-back force to the rider's feet. As will be recognized, occurrences of pedal kick-back are most frequent during use of the bicycle on off-road, uneven terrain wherein significant shocks are frequently applied to the rear wheel.
The present invention addresses these deficiencies of prior art bicycles including shock absorbing rear assemblies by providing a bicycle wherein the crank assembly is independently suspended relative to the main frame and rear assembly. In the present bicycle, the suspension system for the crank assembly is settled into a neutral position by the weight of the rider upon the bicycle, and interacts with the shock absorbing rear assembly in a manner providing for a significantly more efficient transmission of pedaling force from the rider to the rear wheel. Additionally, due to the crank assembly being independently suspended relative to the main frame and shock absorbing rear assembly of the bicycle, occurrences of pedal kick-back are substantially reduced when the rear wheel encounters a bump or other obstruction.